AIM:To investigate the in vitro effects and mechanism of action of cinobufacini on apoptosis of lens epithelial cells (LEC). METHODS:Rabbit LEC were cultured for 72 hours with cinobufacini at different concentrations(0.0[control],0.1,0.2, 0.3mg/L).The inhibition ratio of cinobufacini acting on LEC was analyzed by ethyl thiazolyl tetrazolium(MTT);the changes in DNA structure,by electrophoresis,and the apoptosis rate,by flow cytometry.The mRNA expression of apoptosis-related genes bcl-2 and bax was examined using the reverse transcription-polymerase chain reaction(RT-PCR). RESULTS:At concentrations of 0.1mg/L-0.3mg/L,cinobufacini inhibited LEC proliferation.The inhibition ratio increased as the concentration of the drug increased.The typical DNA-ladders on electrophoretic gels were observed for extracts of LEC in the treated groups.The higher the drug concentration(0.1,0.2,and 0.3mg/L)was,the higher the apoptosis rate(20.47±0.65%,27.14±0.95%,and 33.49±0.77%,respectively)would be.The apoptosis rates in these groups were significantly different from those of the control group(P<0.01).With the drug concentration increasing,the mRNA expression levels of the pro-apoptotic bax increased, whereas those of the anti-apoptotic bcl-2decreased. CONCLUSION:Cinobufacini can notably induce apoptosis of LEC by decreasing the ratio of bc/-2 to bax in vitro.With its low toxicity,this medication may be effective in the prevention and treatment of posterior capsule opacification. A to investigate the in vitro effects and mechanism of action of cinobufacini on apoptosis of lens epithelial cells (LEC). METHODS: Rabbit LEC were cultured for 72 hours with cinobufacini at different concentrations (0.0 [control], 0.1, 0.2, 0.3 mg / L). The inhibition ratio of cinobufacini acting on LEC was analyzed by ethyl thiazolyl tetrazolium (MTT); the changes in DNA structure, by electrophoresis, and the apoptosis rate, by flow cytometry. The mRNA expression of apoptosis-related genes bcl- 2 and bax was examined using the reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: At concentrations of 0.1 mg / L to 0.3 mg / L, cinobufacini inhibited LEC proliferation. Inhibition ratio increased as the concentration of the drug increased The typical DNA-ladders on electrophoretic gels were observed for extracts of LEC in the treated groups. Higher the drug concentration (0.1, 0.2, and 0.3 mg / L) was, the higher the apoptosis rate (20.47 ± 0.65%, 27.14 ± 0.95%, and 33.49 ± 0.77%, respectively) would be. A poptosis rates in these groups were significantly different from those of the control group (P <0.01) .With the drug concentration increasing, the mRNA expression levels of the pro-apoptotic bax increased, those of the anti-apoptotic bcl-2 decreased. CONCLUSION : Cinobufacini can notably induce apoptosis of LEC by decreasing the ratio of bc / -2 to bax in vitro. With its low toxicity, this medication may be effective in the prevention and treatment of posterior capsule opacification.